Buggy code:
private Button btn_Stop ; private Button btn_Delete ; private Spinner dropdown ; private String curCustomCmd = "" ; @ Override protected void onCreate ( Bundle savedInstanceState ) { super . onCreate ( savedInstanceState ) ; setContentView ( activity_light_controller ) ; tv = ( ( TextView ) ( findViewById ( textView ) ) ) ; tv . setMovementMethod ( ScrollingMovementMethod . getInstance ( ) ) ; btnColourPickRed = ( ( Button ) ( findViewById ( btnRed ) ) ) ; btnColourPickGreen = ( ( Button ) ( findViewById ( btnGreen ) ) ) ; btnColourPickBlue = ( ( Button ) ( findViewById ( btnBlue ) ) ) ; btnColourPickCyan = ( ( Button ) ( findViewById ( btnCyan ) ) ) ; btnColourPickYellow = ( ( Button ) ( findViewById ( btnYellow ) ) ) ; btnColourPickMagenta = ( ( Button ) ( findViewById ( btnMagenta ) ) ) ; btn_Start = ( ( Button ) ( findViewById ( R . id . btn_Start ) ) ) ; btn_Rec = ( ( Button ) ( findViewById ( R . id . btn_Rec ) ) ) ; btn_Save = ( ( Button ) ( findViewById ( R . id . btn_Save ) ) ) ; btn_Stop = ( ( Button ) ( findViewById ( R . id . btn_Stop ) ) ) ; btn_Delete = ( ( Button ) ( findViewById ( btn_Del ) ) ) ; btnColourPickRed . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { if ( recordModeState ) { dropdown . setEnabled ( true ) ; disabledLightBtns ( false ) ; } else { BluetoothGattCharacteristic characteristic = map . get ( UUID_BLE_SHIELD_TX ) ; mBluetoothLeService . writeCharacteristic ( characteristic , "k,0000;?" ) ; } } } ) ; btnColourPickGreen . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { if ( recordModeState ) { dropdown . setEnabled ( true ) ; disabledLightBtns ( false ) ; } else { BluetoothGattCharacteristic characteristic = map . get ( UUID_BLE_SHIELD_TX ) ; mBluetoothLeService . writeCharacteristic ( characteristic , "v,0000;?" ) ; } } } ) ; btnColourPickBlue . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { if ( recordModeState ) { dropdown . setEnabled ( true ) ; } else { BluetoothGattCharacteristic characteristic = map . get ( UUID_BLE_SHIELD_TX ) ; mBluetoothLeService . writeCharacteristic ( characteristic , "m,0000;?" ) ; } } } ) ; btnColourPickCyan . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { if ( recordModeState ) { dropdown . setEnabled ( true ) ; disabledLightBtns ( false ) ; } else { BluetoothGattCharacteristic characteristic = map . get ( UUID_BLE_SHIELD_TX ) ; mBluetoothLeService . writeCharacteristic ( characteristic , "t,0000;?" ) ; } } } ) ; btnColourPickYellow . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { if ( recordModeState ) { dropdown . setEnabled ( true ) ; disabledLightBtns ( false ) ; } else { BluetoothGattCharacteristic characteristic = map . get ( UUID_BLE_SHIELD_TX ) ; mBluetoothLeService . writeCharacteristic ( characteristic , "r,0000;?" ) ; } } } ) ; btnColourPickMagenta . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { if ( recordModeState ) { dropdown . setEnabled ( true ) ; disabledLightBtns ( false ) ; } else { BluetoothGattCharacteristic characteristic = map . get ( UUID_BLE_SHIELD_TX ) ; mBluetoothLeService . writeCharacteristic ( characteristic , "a,0000;?" ) ; } } } ) ; btn_Start . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { if ( recordModeState ) { dropdown . setEnabled ( true ) ; disabledLightBtns ( false ) ; } else { BluetoothGattCharacteristic characteristic = map . get ( UUID_BLE_SHIELD_TX ) ; <START_BUG> mBluetoothLeService . writeCharacteristic ( characteristic , "m,0100;v,0100;k,0100;?" ) ; <END_BUG> } } } ) ; btn_Rec . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { recordMode ( true ) ; } } ) ; btn_Save . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { recordMode ( false ) ; } } ) ; btn_Stop . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { } } ) ; btn_Delete . setOnClickListener ( new View . OnClickListener ( ) { @ Override public void onClick ( View view ) { } } ) ; Intent intent = getIntent ( ) ; mDeviceAddress = intent . getStringExtra ( EXTRA_DEVICE_ADDRESS ) ; mDeviceName = intent . getStringExtra ( EXTRA_DEVICE_NAME ) ; Intent gattServiceIntent = new Intent ( this , RBLService . class ) ; bindService ( gattServiceIntent , mServiceConnection , BIND_AUTO_CREATE ) ; dropdown = ( ( Spinner ) ( findViewById ( lst_DropdownTime ) ) ) ; String [ ] items = new String [ ] { "1" , "2" , "three" } ; ArrayAdapter < String > adapter = new ArrayAdapter < String > ( this , layout . simple_spinner_item , items ) ; dropdown . setAdapter ( adapter ) ; dropdown . setOnItemSelectedListener ( new AdapterView . OnItemSelectedListener ( ) { @ Override public void onItemSelected ( AdapterView < ? > parent , View view , int position , long id ) { disabledLightBtns ( true ) ; } @ Override public void onNothingSelected ( AdapterView < ? > parent ) { } } ) ; } private void disabledLightBtns ( Boolean setOn ) { } private void recordMode ( Boolean setOn ) { } @ Override public boolean onCreateOptionsMenu ( Menu menu ) { } @ Override public boolean onOptionsItemSelected ( MenuItem item ) { }

Fix:
mBluetoothLeService . writeCharacteristic ( characteristic , "m,1000;v,1000;k,1000;?" ) ;